1. 1 제 12 장 프로세스 사이의 통신

2. 2 Objectives describe how pipes are used for IPC define the two kinds of pipes use the system calls used with pipes network programming with socket system call

3. 3 IPC using Pipes IPC using regular files unrelated processes can share fixed size life-time lack of synchronization IPC using pipes for transmitting data between related processes unidirectional communication can transmit an unlimited amount of data automatic synchronization on open()

4. 4 IPC using Pipes data transmitting data is written into pipes using write() system call data is read from a pipe using read() system call automatic blocking when full or empty types of pipes (unnamed) pipes named pipes

5. 5 Example % who | sort

6. 6 System Calls int pipe(int fd[ ])

7. 7 System Calls 전형적인 사용법 1) a process creates a pipe 2) fork child process 3) the writer closes its read pipe descriptor, and the reader closes its write pipe descriptor 4) transmitting data via pipe using write() and read() system call 5) each process closes its active pipe descriptor

8. 8 Pipe after fork fd[1] Pipe fd[0] fd[1] ParentChild

9. 9 Sending messages from child to parent #include #define READ 0 #define WRITE 1 char* phrase = “Stuff this in your pipe and smoke it”; main( ) { int fd[2], bytesRead; char message[100]; pipe(fd); if (fork() ==0) { close(fd[READ]); write(fd[WRITE], phrase, strlen(phrase)+1); close(fd[WRITE]); } else { close(fd[WRITE]); bytesRead = read(fd[READ], message, 100); printf(“Read %d bytes: %s\n”, bytesRead,message); close(fd[READ]); }

10. 10 Example #include #define READ 0 #define WRITE 1 main(argc, argv ) int argc; char* argv[]; { int fd[2]; pipe(fd); if (fork() ==0) { close(fd[READ]); dup2(fd[WRITE],1); close(fd[WRITE]); execlp(argv[1], argv[1], NULL); perror(“Connect”); } else { close(fd[WRITE]); dup2(fd[READ],0); close(fd[READ]); execlp(argv[2], argv[2], NULL); perror(“Connect”); }

11. 11 Named pipes Why named pipes ? they have a name that exists in the file system they may be used by unrelated processes they exist until explicitly deleted How to create named pipes ? by using the UNIX mknod commond with the p option $mknod myPipe p $ chmod ug+rw myPipe $ ls -lg myPipe by using the mknod() system call int mknod(char* path, int mode, int dev) return 0 if successful, -1 otherwise

12. 12 How to communicate via pipes ? Writer process should open a named pipe for write-only write data using write() system call Reader process should open a named pipe for read-only read data using read() system call

13. 13 Example:Reader #include main( ) { int fd; char str[100]; unlink(“aPipe”); mknod(“aPipe”, S_IFIFO, 0); chmod(“aPipe”, 0660); fd = open(“aPipe”, O_RDONLY); while (readLine(fd, str)) printf(“%s\n”, str); close(fd) }

14. 14 Example:Reader readLine(fd, str) int fd; char *str; { int n; do { n = read(fd, str, 1); } while (n>0 && *str++ != NULL); return (n>0); }

15. 15 Example:Writer #include main( ) { int fd, messageLen, i; char message[100]; sprintf(message, “Hello from PID %d”, getpid()); messageLen= strlen(message)+1; do { fd = open(“aPipe”, O_WRONLY); if (fd == -1) sleep(1); } while(fd == -1); for (i =1; i<= 3; i++) { write(fd, message, messageLen); sleep(3); } close(fd); }

16. 16 Sockets Socket bidirectional connection process communication based on client-server model AF_UNIX socket an interprocess communication mechanism between processes on the same UNIX machine AF_INET socket an interprocess communication mechanism between processes across network

17. 17 The socket connection Server Client 1. Sever creates a named socket 2. Client creates an unnamed socket and request a connection 3. Server makes a connection. Server retains original named socket

18. 18 Client-Server Model Server – Server creates a named socket using socket() – Server makes a pending queue using listen() – Server accept() from a client connection() – When a socket isconnected the server usually fork() a child process to converse with the client Client – Client creates an unnamed socket using socket() – Client requests a connection using connect() – Client makes a connection when server accept( ) it.

19. 19 Creating a Socket 소켓 만들기 int socket (int domain, int type, int protocol ) domain AF_UNIX (the clients and server must be in the same machine) AF_INET(the and server may be anywhere on the Internet) type SOCK_STREAM protocol DEFAULT _PROTOCOL Example serverFd = socket(AF_UNIX, SOCK_STREAM, DEFAULT _PROTOCOL);

20. 20 Naming a Socket 소켓에 이름 ( 주소 ) 주기 int bind(int fd, struct sockaddr* address, int addressLen ) bind the unnamed socket with fd to a name in address address is a pointer to struct sockaddr_un sun_family = AF_UNIX sun_path = name of the socket struct sockaddr_in sin_family = AF_INET sin_port = the port number of Internet socket sin_addr = 32-bit IP address sin_zero = leave empty addressLen = length of address structure

21. 21 Example serverUNIXAddress.sun_family = AF_UNIX; strcpy(serverUNIXAddress.sun_path, “recipe”); unlink(“recipe”); bind(serverFd, serverSockAddrPtr, serverLen);

22. 22 Creating a Socket Queue 소켓 큐 생성 specify the maximum number of pending connections on a socket int listen (int fd, int queueLength ) example listen(serverFd, 5);

23. 23 Making the Connection 소켓에 연결 요청 int connect (int fd, struct sockaddr* address, int addressLen ) attempts to connect to a server socket whose address is in a structure pointed to by address If successful, fd may be used to communicate with the server’s socket

24. 24 Accepting a Client 소켓 연결 요청 수락 int accept (int fd, struct sockaddr* address, int* addressLen ) (1) listen to the named server socket referenced by fd (2) wait until a client connection request is received (3) creates an unnamed socket with the same attributes as the original server socket, and connects it to the client’s socket. (4) When a connection is made, address is set to the address of the client socket and addressLen is set to the actual size (5) return a new file descriptor

25. 25 Chef Server-Cook Client %chef & %cook spam, spam, spam, and spam %cook spam, spam, spam, and spam

26. 26 Example : Chef Server(1/3) #include #define DEFAULT_PROTOCOL 0 main ( ) { int serverFd, clientFd, serverLen, clientLen; struct sockaddr_un serverUNIXAddress; struct sockaddr_un clientUNIXAddress; struct sockaddr* serverSockAddrPtr; struct sockaddr* clientSockAddrPtr; signal(SIGCHLD, SIG_IGN);

27. 27 Example : Chef Server(2/3) serverSockAddrPtr= (struct sockaddr*) &serverUNIXAddress; serveLen = sizeof(serverUNIXAddress); clientSockAddrPtr = (struct sockaddr*) &clientUNIXAddress; clientLen = sizeof(clientUNIXAddress); serverFd = socket(AF_UNIX, SOCK_STREAM, DEFAULT_PROTOCOL); serverUNIXAddress.sun_family = AF_UNIX; strcpy(serverUNIXAddress.sun_path, “receipe”); unlink(“receipe”); bind(serverFd, serverSockAddrPtr, serverLen); listen(serverFd, 5);

28. 28 Example:Chef Server(3/3) while (1) { clientFd = accept(serverFd, clientSockAddrPtr, &clientLen); if (fork ( ) == 0) { writeRecipe(clientFd); close(clientFd); exit (0); } else close(clientFd); } writeRecipe(fd) int fd; { static char* line1 =“spam, spam, spam, spam,”; static char* line2 = “spam and spam.”; write(fd, line1, strlen(line1)+1); write(fd, line2, strlen(line2)+1); }

29. 29 Example:Cook Client(1/3) #include #define DEFAULT_PROTOCOL 0 main ( ) { int clientFd, serverLen, result; struct sockaddr_un serverUNIXAddress; struct sockaddr* serverSockAddrPtr; serverSockAddrPtr= (struct sockaddr*) &serverUNIXAddress; serverLen = sizeof(serverUNIXAddress);

30. 30 Example:Cook Client(2/3) clientFd = socket(AF_UNIX, SOCK_STREAM, DEFAULT_PROTOCOL); serverUNIXAddress.sun_family = AF_UNIX; strcpy(serverUNIXAddress.sun_path, “receipe”); do {result = connect(clientFd, serverSockAddrPtr, serverLen); if (result == -1) sleep(1); } while (result == -1); readRecipe(clientFd); close(clientFd); exit(0) }

31. 31 Example:Client(3/3) readRecipe(fd); int fd; { char str[200]; while (readLine(fd, str)) printf(“%s\n”, str); } readLine(fd, str) int fd; char* str; { int n; do { n = read(fd, str, 1); } while(n>0 && *str++ != NULL); return(n > 0); }

32. 32 Internet Sockets A client for Internet Time Listing Internet socket is specified by two values: a 32-bit IP address a 16-bit port number, which specifies a particular port on the host port number 13 is used to echo the host’s time

33. 33 Internet Sockets A client for Internet Time Listing Internet socket address structure struct sockaddr_in sin_family = AF_INET sin_port = 16bit port number of the Internet socket sin_addr = 32-bit IP address, which is a structure of type in_addr sin_zero = leave empty

34. 34 Example:Internet Time Listing % inettime Host name (q= quit, s= self): s Self host name is cs Internet Address= 203.252.195.1 The time on the target port is … Host name (q= quit, s= self): monkey Internet Address= 203.252.195.246 The time on the target port is … Host name (q= quit, s= self): 203.252.195.247 The time on the target port is …

35. 35 Client:Internet Time Listing(1/4) #include #define DAYTIME_PORT 13 #define DEFAULT_PROTOCOL 0 main ( ) { int clientFd, serverLen, result; struct sockaddr_in serverINETAddress; struct sockaddr* serverSockAddrPtr; unsigned long inetAddress;

36. 36 Client:Internet Time Listing(2/4) serverSockAddrPtr= (struct sockaddr*) &serverINETAddress; serverLen = sizeof(serverINETAddress); while (1) { inetAddress = promptForINETAddress( ); if (inetAddress == 0) break; bzero((char*)&serverINETAddress, sizeof(serverINETAddress)); serverINETAddress.sin_family = AF_INET; serverINETAddress.sin_addr.s_addr = inetAddress; serverINETAddress.sin_port = htons(DAYTIME_PORT); clientFd = socket(AF_INET, SOCK_STREAM, DEFAULT_PROTOCOL);

37. 37 Client:Internet Time Listing(3/4) do { result = connect(clientFd, serverSockAddrPtr, serverLen); if (result == -1) sleep(1); } while (result == -1); readTime(clientFd); close(clientFd); } exit(0); }

38. 38 Client:Internet Time Listing(4/4) readTime(fd) int fd; {char str[200]; printf(“The time on the target port is”); while (readLine(fd, str)) printf(“%s\n”, str); } readLine(fd, str) int fd; char* str; { int n; do { n = read(fd, str, 1); } while (n > 0 && *str++ != ‘\n’); return(n > 0); }

39. 39 promptForINETAddress unsigned long promptForINETAddress() { char hostName[100]; unsigned long inetAddress; do {printf(“Host name (q=quit, s =self):”); scanf(“%s”, hostName); if (strcmp(hostName, “q”) == 0) return(0); inetAddress = nameToAddr(hostName); if (inetAddress == 0) printf(“Host name not found\n”); } while(inetAddress == 0); return(inetAddress); }

40. 40 nameToAddr unsigned long nameToAddr(name) char* name; { char hostName[100]; struct hostent* hostStruct; struct in_addr* hostNode; if(isdigit(name[0])) return(inet_addr(name)); if (strcmp(name, “s”) == 0) { gethostname(hostName, 100); printf(“Self host name is %s\n”,hostName); } else strcpy(hostName, name); hostStruct = gethostbyname(hostName); if (hostStruct == NULL) return(0); hostNode = (struct in_addr*) hostStruct->h_addr; printf(“Internet Address = %s\n”,inet_ntoa(*hostNode)); return(hostNode->s_addr); }

41. 41 Miscellaneous system calls unsigned long inet_addr (char* string ) returns the 32-bit IP address that corresponds to the A.B.C.D formt string int gethostname (char* name, int nameLen ) sets the character array name, of length nameLen to a null-terminated string equal to the local host’s name

42. 42 Miscellaneous system calls struct hostent* gethostbyname (char* name ) searches the “/etc/hosts” file and returns a pointer to a hostent structure that describes the file entry associated with the string name char* inet_ntoa (struct in_addr address) returns a pointer to a string that describes address in the format A.B.C.D.

43. 43 Internet Server(1/3) #include #define DEFAULT_PROTOCOL 0 main ( ) { int serverFd, clientFd, serverLen, clientLen; struct sockaddr_in serverINETAddress; struct sockaddr_in clientINETAddress; struct sockaddr* serverSockAddrPtr; struct sockaddr* clientSockAddrPtr;

44. 44 Internet Server(2/3) int port = 13; serverFd = socket(AF_INET, SOCK_STREAM, DEFAULT_PROTOCOL); serverLen = sizeof(serverINETAddress); bzero((char*) &serverINETAddress, serverLen); ServerINETAddress.sin_family = AF_INET; serverINETAddress.sin_addr.s_addr = htonl(INADDR_ANY); serverINETAddress.sin_port = htons(port); serverSockAddrPtr = (struct sockaddr*) &serverINETAddress; bind(serverFd, serverSockAddrPtr, serverLen); listen(serverFd, 5); clientLen = sizeof(clientINETAddress); clientSockAddrPtr = (struct sockaddr*) clientINETAddress

45. 45 Internet Server(3/3) while (1) { clientFd = accept(serverFd, clientSockAddrPtr, &clientLen); if (fork ( ) == 0) { service(clientFd); close(clientFd); exit (0); } else close(clientFd); }